@GJM shoots A LOT, and one would be wise to listen and consider.
For me, with a Colt carbine, I’ve fired two mags (one 18, one 28)of my particular choice. In my situation(suburban residential, travel to rural settings on occasion) that’s what I anticipate might probably be called for”YMMV”.
If you have the wherewithal to run a higher round count, then by all means go for it. Personally, I believe if a brand name long arm(Colt, BCM, Daniel Defense, etc.) cannot get through two reputable mags(Magpul,etc.) in a relatively clean and lubed condition, time to seek another carbine.
I ascribe to the download of 2 rounds because Clint Smith mentioned it years ago at a class and it hasn’t failed me yet!